A capacitance detection apparatus for detecting approach of an object such as a human body on the basis of a change of capacitance is conventionally known. In these years, such capacitance detection apparatus is utilized in a system for controlling open/close of a boarding door of a vehicle. In such system, the capacitance detection apparatus is utilized for detecting a trigger of an unlock operation. Specifically, when a user approaches a vehicle, correspondence between identification (ID) code of a vehicle side and that of a mobile apparatus of the user is checked, and the mode of the vehicle transfers into an unlock permission mode. Then, when the user touches an unlock sensor (electrode) provided in an outside door handle of the vehicle at this time, the vehicle side detects a change of capacitance of the unlock sensor electrode and performs an unlock operation. In other words, the capacitance detection apparatus detects an intention of the user to unlock the door utilizing an output from the unlock sensor (change of capacitance) (for example, as described in JP2005-134178A).
In such capacitance detection apparatus, in order to judge, on the basis of the detected change of capacitance, whether an object to be detected approaches in actual or not, it needs to be considered whether a difference between values associated with the change of capacitance, currently detected and detected in the past, is equal to or more, or equal to or less, than the threshold value. In other words, because an approaching object induces characteristic profiles in records of the capacitance change, judging an approach of an object without correctly detecting the characteristic profiles tends to lead to an operational error. Accordingly, in order for reliably judging whether a currently detected change of a value associated with the capacitance change is caused by an approach of an object to be detected, a value associated with the past capacitance change needs to be referred.
Generally, for detecting an approach of a human body, a value associated with the capacitance change recorded earlier, by approximately 250 millisecond, than the profile of the capacitance change caused by the approach of the human body needs to be referred. This causes a difficulty for detecting a human body by the capacitance detection apparatus before 250 millisecond lapses from a start time of the capacitance detection apparatus.
However, in general cases in which the capacitance detection apparatus is utilized for unlocking the vehicle as described above, the capacitance detection apparatus is not always in operation. The capacitance detection apparatus starts operation after correspondence between an ID code of a vehicle and that of a user is checked and the ID of the user is identified. Accordingly, before 250 millisecond lapses from when the user is identified, a human body cannot be detected. Therefore, the user cannot unlock the door until 250 millisecond lapses after the capacitance detection apparatus starts operation, even when the user wants to unlock the vehicle earlier. Accordingly, in a case where this kind of the capacitance detection apparatus is applied to unlock of the vehicle, improvement in response has been desired.
A need thus exists for a capacitance detection apparatus, which has improved response for detecting approach of an object at an initial stage after the capacitance detection apparatus starts operation. The present invention has been made in view of the above circumstances and provides such a capacitance detection apparatus.